ANTI-ROTATION SHROUD FOR TURBINE ENGINES
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The field of the invention relates to turbine engines generally, and more
particularly to certain new and useful advances in anti-rotation features for turbine
shrouds, of which the following is a specification, reference being had to the drawings
accompanying and forming a part of the same.
Description of Related Art
[0002] Turbine engines comprise an airfoil attached to a rotor that rotates about a
predetermined axis of rotation. An annular shroud is circumferentially positioned about
and spaced apart from the airfoil. An annular split turbine case is circumferentially
positioned about and coupled with the shroud. Additionally, an anti-rotation device is
added and coupled with the shroud to prevent the shroud from rotating during normal
engine operations. However, this anti-rotation device is an extra part that must be
installed, disassembled and/or maintained in addition to other components of the turbine
engine.
BRIEF SUMMARY OF THE INVENTION
[0003] The present disclosure describes embodiments of an improved shroud for
turbine engines with 180 degree split turbine casings. The shroud has an integrated antirotation
device that prevents circumferential movement of the shroud during normal
engine operation, and which allows for circumferential installation. Since the antirotation
device is an integral part of the shroud, no additional parts are necessary for
assembly or disassembly. Moreover, existing turbine cases can be reworked to accept the
anti-rotation device and yet still be backwards compatible with original shroud designs.
[0004] Other features and advantages of the disclosure will become apparent by
reference to the following description taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0005] Reference is now made briefly to the accompanying drawings, in which:
[0006] Figure 1 is a perspective view of a portion of an improved turbine shroud
configured for use in a turbine engine;
[0007] Figure 2 is a partial, close-up view of an anti-rotation device integrally
formed with the improved turbine shroud of Figure 1;
[0008] Figure 3 is another partial, close-up view of the anti-rotation device of
Figure 2;
[0009] Figure 4 is a plan view of an interior surface of the improved turbine
shroud of Figure 1;
[0010] Figure 4A is an end view of the improved turbine shroud of Figures 1 and
4;
[001 1] Figure 4B is a forward side view of the improved turbine shroud of
Figures 1 and 4;
[0012] Figure 4C is another end view of the improved turbine shroud of Figures 1
and 4;
[0013] Figure 4D is an aft side view of the improved turbine shroud of Figures 1
and 4;
[0014] Figure 4E is a plan view of a back surface of the improved turbine shroud
of Figures 1 and 4;
[0015] Figure 5 is a perspective view of a section of an improved turbine case that
is configured to couple with the improved turbine shroud of Figures 1, 4, 4A, 4B, 4C, 4D,
and 4E;
[0016] Figure 6 is a perspective view of a section of the improved turbine case of
Figure 5 illustrating its coupling with the improved turbine shroud of Figures 1, 4, 4A,
4B, 4C, 4D and 4E and a second stage nozzle, a portion of which overlaps an antirotation
device integrally formed with the improved turbine shroud;
[0017] Figures 7, 8 and 9 are diagrams illustrating assembly of an embodiment of
the improved turbine shroud of Figures 1, 4, 4A, 4B, 4C, 4D and 4E and engagement of
the integrally formed anti-rotation device with a channel formed in an improved turbine
case.
[0018] Figure 10 is a plan view of an interior surface of a second embodiment of
an improved turbine shroud;
[0019] Figure 11 is a plan view of a back surface of the second embodiment of the
improved turbine shroud of Figure 10;
[0020] Figure 12 is a perspective view of a section of another improved turbine
case that is configured to couple with the improved turbine shroud of Figures 10 and 11;
[0021] Figure 13 is a cross-sectional view of a portion of the improved turbine
case of Figure 12, taken along the line A-A' in Figure 12; and
[0022] Figure 14 is a perspective view of a section of the improved turbine case
of Figure 12 illustrating its coupling with the improved turbine shroud of Figures 10 and
11 and a second stage nozzle, a portion of which overlaps an anti-rotation device
integrally formed with the improved turbine shroud.
[0023] Like reference characters designate identical or corresponding components
and units throughout the several views, which are not to scale unless otherwise indicated.
DETAILED DESCRIPTION OF THE INVENTION
[0024] As used herein, an element or function recited in the singular and
proceeded with the word "a" or "an" should be understood as not excluding plural said
elements or functions, unless such exclusion is explicitly recited. Furthermore,
references to "one embodiment" of the claimed invention should not be interpreted as
excluding the existence of additional embodiments that also incorporate the recited
features.
[0025] Figure 1 is a perspective view of a portion of an improved turbine shroud
100 configured for use in a turbine engine. Figure 2 is a partial, close-up view of an antirotation
device 140 integrally formed with the improved turbine shroud 100 of Figure 1.
Figure 3 is another partial, close-up view of the anti-rotation device 140 of Figure 2.
Figure 4 is a plan view illustrating an interior surface 142 of the improved turbine shroud
100 of Figure 1. Figure 4A is an end view of the improved turbine shroud 100 of Figures
1 and 4. Figure 4B is a forward side view of the improved turbine shroud 100 of Figures
1 and 4. Figure 4C is another end view of the improved turbine shroud 100 of Figures 1
and 4. Figure 4D is an aft side view of the improved turbine shroud 100 of Figures 1 and
4. Figure 4E is a plan view illustrating shroud backing surface 141 of the improved
turbine shroud 100 of Figures 1 and 4.
[0026] Referring to Figures 1, 2, 3, 4, 4A, 4B, 4C, 4D, and 4E, the improved
turbine shroud 100 (hereinafter "shroud 100") has an annular shape, although only a
portion thereof is shown in the Figures for ease of illustration and description. As
persons skilled in the aircraft engine and power generation fields will appreciate, the
improved turbine shroud 100 is a component of a turbine engine. When installed in a
turbine engine, the improved turbine shroud is spaced slightly apart from and positioned
coaxially around an airfoil that is attached to a rotor. When the rotor rotates at a high
speed about a predetermined central axis of rotation, the airfoil spins at high speeds
within the annulus formed by the assemblage of the improved turbine shroud, which is
supported by a split annular turbine case that is positioned coaxially around it.
[0027] The shroud 100 comprises several sections: a body 130 and two rails
connected therewith - an aft rail 131 and a forward rail 133. As used herein, the term
"aft" refers to a downstream portion of a turbine engine, and the term "forward" (also,
"fwd") refers to an upstream portion of a turbine engine. The aft rail 131 has an aft edge
105. The forward rail 133 has a forward edge 107. As shown in Figures 1, 4A and 4C,
the body 130 has a cavity 135 on its interior surface 142. The cavity 135 is an indented
portion of the body 130 between sidewalls 143 that connect the aft rail 131 and the
forward rail 133 with the body 130. Consequently, the shroud backing surface 141 of the
body 130 occupies a different plane than the aft rail 131 and the forward rail 133. The
cavity 135 is configured to contain an open-faced honeycomb core 103. The honeycomb
core is comprised of corrugated sheet metal ribbon which is formed into hexagonal (6
sided) cells of a uniform size arranged in a staggered formation, where each cell is
surrounded by 6 adjacent cells that share a common wall with one another. The
honeycomb core 103 is connected to cavity 135 through a metal braze operation. This
honeycomb structure provides a dual function; the first is to provide a sacrificial material
to prevent damage to the turbine airfoil in the event of rub/contact/incursion between the
rotating and static components of the engine during operation; and second to maintain a
small tip clearance between the static and rotating components thus improving the engine
performance by reducing flowpath air leakage around the tip of the airfoil.
[0028] One or more supports 109, or ship laps, are coupled with the shroud
backing surface 141 of the body 130 and the aft rail 131. Each support 109 has a base
137 configured to couple with the shroud backing surface 141 of the body 130 of the
shroud 100, a support sidewall 138 coupled with the base 137, and a support rail 139
coupled with the support sidewall 138. Each support 109 is formed of a nickel or cobalt
based sheet metal and is coupled with the shroud 100 using tack-welds or alternate
positioning techniques in preparation for metal braze operation to permanently
bond/adhere each support 109 to the shroud backing surface 141. Additionally, each
support 109 functions to retain the shroud 100 radially within the casing assembly
ensuring the shroud 100 is coaxial with the rotating airfoil.
[0029] In one embodiment, the forward rail 133 of the shroud 100 has an antirotation
device 140 integrally formed therein. The anti-rotation device 140 comprises a
fixed base end 111, a resilient portion 110, and a free end 113 that comprises a tab 120.
A base gap 119 having a predetermined shape, width and length separates the base end
111 of the anti-rotation device 140 from a first portion of the forward rail 133 that adjoins
the sidewall 143. The base gap 119 serves to reduce the stresses at the base of the antirotation
feature 140 to be within the material capability of the shroud 100 A second gap
117 of predetermined length and width extends from the base gap 119, substantially
parallel a forward edge 107 of the forward rail 133, and past an end surface 121 of the
free end 113 of the resilient portion 110. The second gap 117 separates the resilient
portion 110 and free end 113 of the anti-rotation device 140 from a second portion of the
forward rail 133 that adjoins the sidewall 143. Consequently, the resilient portion 110 is
flexible and biased to return the free end 113 to the position shown in Figure 1 if the free
end 113 with the tab 120 and/or the resilient portion 110 are moved relative to the
forward rail 133.
[0030] As shown in Figures 1, 2, 3, 4 and 4E, a third gap 115, or cut-out,
separates the end surface 121 of the free end 113 of the resilient portion 110 from an
adjacent third portion of the forward rail 133. The third gap 115 is dimensioned and
configured to permit the free end 113 of the anti-rotation device 140 to move relative to
the forward rail 133. In one embodiment, the third gap 115 is orthogonal to the second
gap 117.
[0031] Additionally, the tab 120 protrudes outwardly from the shroud backing
surface 141 of the forward rail 133 a predetermined distance. The tab 120 has an end
surface 121 of a height equal, or about equal, to a thickness of the forward rail 133.
Coupled with the end surface 121 is an angled surface 123, which slopes at a
predetermined angle towards the base end 111. The angled surface 123 couples with a
main surface 125. In turn, the main surface 125 couples with an orthogonal, or nearly
orthogonal, projection surface 127, which couples with the resilient portion 110.
[0032] Figure 5 is a perspective view of a section of an improved split line turbine
case 200 (hereinafter, "case 200") that is configured to couple with the improved turbine
shroud 100 of Figures 1, 4, 4A, 4B, 4C, 4D, and 4E. Depending on the embodiment, the
case 200 comprises a metal, a metal alloy, a composite material or a combination thereof
Referring to Figure 5, although only a portion is shown for clarity and ease of illustration,
the improved turbine case 200 is annular and is formed with at least 2 halves, of 180
degrees, where the axis of case 200 is collinear with the engine centerline and coaxial
with the rotation of the airfoils. Additionally case 200 has a plurality of parallel grooves,
channels and rails formed therein. For example, a first shroud groove 209, e.g., a first
stage shroud groove 209, is formed adjacent and substantially parallel a forward edge 207
of the case 200. In one embodiment, the shroud groove 209 comprises a first rail 225,
e.g., a forward rail 225, and a second rail 227, e.g., an aft rail 227, that are spaced apart to
form a cavity 231 therebetween. Additionally, first channels 229 are formed in
corresponding upper portions of the forward rail 225 and the aft rail 227. Additionally,
the aft rail 227 comprises a second channel 233 formed in a lower portion thereof, below
and on a side of the aft rail 227 opposite the first channels 229. The case 200 further
comprises a third rail 215, e.g., a nozzle rail 215 that is positioned between and spaced
apart from the aft rail 227 and a shroud ledge 223. In other words, the nozzle rail 215 is
spaced aft and apart from the aft rail 227 and also spaced apart from and forward of the
shroud ledge 223, as illustrated in Figure 5. One or more notches 217 are formed in an
upper portion of the nozzle rail 215. Each notch 217 has a first surface 235 positioned
opposite a second surface 237. The first surface 235 is configured to engage at least the
projection surface 127 of the tab 120 of the anti-rotation device 140 of Figures 1, 2, 3, 4,
4A, 4B, 4C, 4D and 4E. The second surface 237 is proximate, and may contact, the
angled surface 123 of the tab 120 of the anti-rotation device 140 of Figures 1, 2, 3, 4, 4A,
4B, 4C, 4D and 4E during assembly and disassembly of a turbine engine.
[0033] The space between the aft rail 227 and the nozzle rail 215 forms a nozzle
groove 2 11, for a second stage nozzle (not shown in Figure 5). The space between the
nozzle rail 215 and the shroud ledge 223 forms a second shroud groove 213, e.g., a
second stage shroud groove 213. The second shroud groove 213 has a surface 219 that is
positioned below an upper surface of the nozzle rail 215 and an upper surface of the
shroud ledge 223. As illustrated, the shroud ledge 223 is adjacent and parallel to the aft
portion 205 of the case 200, and includes a ledge 221 along its top, forward edge.
[0034] Figure 6 is a perspective view of a section of the improved turbine case
200 of Figure 5 illustrating its coupling with the improved turbine shroud 100 of Figures
1, 4, 4A, 4B, 4C, 4D and 4E and a second stage nozzle 300, a portion 301 of which
overlaps an embodiment of an anti-rotation device 140 integrally formed with the
improved turbine shroud 100. The second stage nozzle 300 is positioned within the
nozzle groove 2 11. As shown, when installed, the shroud 100 occupies the second
shroud groove 213 of the case 200, with the shroud's aft rail 131 positioned proximate
the aft portion 205 of the case 200 and the shroud's forward rail 133 positioned toward
the forward portion 207 of the case 200. In particular, the shroud's aft rail 131 contacts
the shroud ledge 223, and the shroud's forward rail 133 contacts the nozzle rail 215. The
base 137 of the shroud's support strip 109 does not contact the surface 219 of the second
shroud groove 213 and forms a gap/clearance/cavity with said surface. Moreover, the
support rail 139 of the support strip 109 maintains a clearance fit with the ledge 221
formed along an upper, forward edge of the shroud ledge 223.
[0035] The resilient portion 110 (Figure 1) is biased to mate, or couple, the tab
120 of the anti-rotation device 140 with the notch 217 formed in the nozzle rail 215 of the
turbine case 200. Once installed as shown, the forward rail 133 of the shroud 100,
including the anti-rotation device 140 (Figure 1) and all its components, are overlapped
by a portion 301, e.g. a nozzle overhang 301, of a second stage nozzle 300, which is
positioned within the second stage nozzle groove 2 11. By overlapping the anti-rotation
device 140, the nozzle overhang 301 prevents the tab 120 of the anti-rotation device 140
from disengaging the notch 217 formed in the nozzle rail 215. Accordingly, the coupling
between the tab 120 of the anti-rotation device 140 and the notch 217 formed in the
nozzle rail 215 of the case 200 prevents the shroud 100 from rotating during engine
operation. However, removal of the second stage nozzle 300 during disassembly of the
engine, uncovers the forward rail 133 of the shroud 100, including the anti-rotation
device 140. Thereafter, circumferential rotation of the shroud 100 in a direction opposite
that of normal airfoil rotation causes the second surface 237 (Figure 5) of the notch 217
to contact the angled surface 123 (Figure 5) of the tab 120 of the anti-rotation device 140
and raise the tab 120 of the anti-rotation device 140 up and out of the notch 217.
[0036] Figures 7, 8 and 9 are diagrams illustrating assembly of an embodiment of
the improved turbine shroud 100 of Figures 1, 4, 4A, 4B, 4C, 4D and 4E and engagement
of the integrally formed anti-rotation device 140 with a notch 217 formed in a nozzle rail
215 of an improved turbine case 200. In these Figures, angled lines aft of the nozzle rail
215 represent honeycomb core 103. Arrows 403 represent a direction of airfoil rotation
during normal turbine engine operation. Arrow 400 indicates a direction of
circumferential rotation of the shroud 100 during assembly and/or disassembly. Arrow
205 represents an aft portion of the turbine case 200, and arrow 207 represents a forward
portion of the turbine case 200. In one embodiment, this direction of circumferential
rotation 400 of the shroud 100 is opposite the direction of rotation 403 of the airfoil 401.
[0037] Beginning with Figure 7, a turbine shroud 100 having a forward rail 133
that contacts a nozzle rail 215 of a turbine case 200 is circumferentially rotated in the
direction of assembly represented by arrow 400 until, as shown in Figure 8, the tab 120 of
the anti-rotation device 140 fits within the notch 217 formed in the nozzle rail 215 and
couples with a first surface 235 of the notch 217. As shown in Figure 7, the free end
113 of the anti-rotation device 140 initially rests on an upper surface of the nozzle rail
215 and is thus biased up and a way from the forward rail 133 and nozzle rail 215 to
permit the main surface 125 and/or the angled surface 123 of the tab 120 of the antirotation
device 140 to slide along the nozzle rail 215 in the turbine case 200 during
assembly or disassembly. When the free end 113 of the anti-rotation device 140 is over
the notch 217, spring action of the biased resilient portion 110 (Figure 1) moves the tab
120 of the anti-rotation device 140 into the notch 217. Since the projection surface 127,
e.g., load bearing surface 127, of the tab 120 is in the same direction of the rotating
airfoil, the shroud 100 is considered to be anti-rotated. Thereafter, the nozzle (300 in
Figure 6) is assembled circumferentially after the shroud 100 is in place. An aft portion
301 of the nozzle 300 will overlap the flow path side of the anti-rotation device 140 thus
preventing the tab 120 and/or the free end 113 of the anti-rotation device 140 from
disengaging the notch 217.
[0038] When the tab 120 of the anti-rotation device 140 fits within the notch 217,
the anti-rotation device 140 is parallel, or substantially parallel, the plane of the forward
rail 133 of the shroud 100 and ready to be overlapped by a portion 301 (Figure 6) of a
nozzle 300 (Figure 6). As shown in Figure 9, vibrations and forces caused by normal
rotation of the airfoil 401 tend to drive at least the projection surface 127 of the tab 120 of
the anti-rotation device 140 and the first surface 235 of the notch 217 closer together.
However, once the tab 120 of the anti-rotation device 140 and the first surface 235 of the
notch 217 engage, further circumferential movement of the shroud 100 in the direction of
airfoil rotation 403 stops.
[0039] Figure 10 is a plan view of an interior surface of a second embodiment of
an improved turbine shroud 100. Figure 11 is a plan view of a back surface of the second
embodiment of the improved turbine shroud of Figure 10. Referring to Figures 10 and
11, this second embodiment is identical to that previously described above with respect to
Figures 1, 2, 3, 4, 4A, 4B, 4C, 4D and 4E, except that the notch 217 that receives the tab
120 of the anti-rotation device 140 is formed in the forward rail 133, instead of in the rail
215 (Figure 5) of the turbine case 200 (Figure 5). The aft rail 131, support strips 109 and
honeycomb 103 are the same as previously described.
[0040] Figure 12 is a perspective view of a section of another improved split
turbine case 200 that is configured to couple with the improved turbine shroud 100 of
Figures 10 and 11. This second embodiment is identical to that previously described
above with respect to Figure 5, except that a portion of the rail 215 has an anti-rotation
device 140, which includes the resilient portion 110. The resilient portion 110 is
separated from the rail 215 by gap 117. The free end 113 of the resilient portion 110
includes the tab 120, which has an angled surface 123 and a main surface 127, as
previously described. The aft portion 205, forward portion 207, aft rail 227, first stage
shroud groove 209, second stage nozzle groove 2 11 and second stage shroud groove 213
are also as previously described.
[0041] Figure 13 is a cross-sectional view of a portion of the improved turbine
case 200 of Figure 12, taken along the line A-A' in Figure 12, that further illustrates the
second embodiment of the anti-rotation device 140 formed in the rail 215 of the improved
turbine case 200. As shown in Figure 13, the free end 113 of the resilient portion 110
includes the tab 120. The tab 120 includes the projection surface 127, which is coupled
with the main surface 125. The main surface 125 is coupled with the angled surface 123.
The angled surface 123 is coupled with the end surface 121. The end surface 121 is
separated from an opposite portion of the rail 215 by the gap 115.
[0042] Figure 14 is a perspective view of a section of the improved split turbine
case 200 of Figure 12 illustrating its coupling with the improved turbine shroud 100 of
Figures 10 and 11 and a second stage nozzle 300, a portion 301 of which overlaps the
anti-rotation device 140 integrally formed with the rail 215 of the improved split turbine
case 200. As shown, when installed, the shroud 100 occupies the second shroud groove
213 of the case 200, with the shroud's aft rail 131 positioned proximate the aft portion
205 of the case 200 and the shroud's forward rail 133 positioned toward the forward
portion 207 of the case 200. In particular, the shroud's aft rail 131 contacts the shroud
ledge 223, and the shroud's forward rail 133 contacts the nozzle rail 215. The base 137
of the shroud's support strip 109 does not contact the surface 219 of the second shroud
groove 213 and forms a gap/clearance/cavity with said surface. Moreover, the support
rail 139 of the support strip 109 maintains a clearance fit with the ledge 221 formed along
an upper, forward edge of the shroud ledge 223.
[0043] The resilient portion 110 is biased to mate, or couple, the tab 120 of the
anti-rotation device 140 with the notch 217 formed in the forward rail 133 of the shroud
100. Once installed as shown, the forward rail 133 of the shroud 100, including the antirotation
device 140 (Figure 1) and all its components, are overlapped by a portion 301,
e.g. a nozzle overhang 301, of a second stage nozzle 300, which is positioned within the
second stage nozzle groove 2 11. By overlapping the anti-rotation device 140, the nozzle
overhang 301 prevents the tab 120 of the anti-rotation device 140 from disengaging the
notch 217 formed in the forward rail 133 of the shroud 100. Accordingly, the coupling
between the tab 120 of the anti-rotation device 140 and the notch 217 prevents the shroud
100 from rotating during engine operation. However, removal of the second stage nozzle
300 during disassembly of the engine, uncovers the forward rail 133 of the shroud 100,
including the anti-rotation device 140. Thereafter, circumferential rotation of the shroud
100 in a direction opposite that of normal airfoil rotation causes a surface of the notch
217 to contact the angled surface 123 of the tab 120 of the anti-rotation device 140 and
move the tab 120 of the anti-rotation device 140 out of the notch 217.
[0044] This written description uses examples to disclose the invention, including
the best mode, and also to enable any person skilled in the art to make and use the
invention. The patentable scope of the invention is defined by the claims, and may
include other examples that occur to those skilled in the art. Such other examples are
intended to be within the scope of the claims if they have structural elements that do not
differ from the literal language of the claims, or if they include equivalent structural
elements with insubstantial differences from the literal languages of the claims.
[0045] Although specific features of the invention are shown in some drawings
and not in others, this is for convenience only as each feature may be combined with any
or all of the other features in accordance with the invention. The words "including",
"comprising", "having", and "with" as used herein are to be interpreted broadly and
comprehensively and are not limited to any physical interconnection. Moreover, any
embodiments disclosed in the subject application are not to be taken as the only possible
embodiments. Other embodiments will occur to those skilled in the art and are within the
scope of the following claims.
CLAIMS
What Is Claimed Is:
1. A split-line turbine case, comprising:
a nozzle rail having a notch therein, the notch configured to receive a tab of an
anti-rotation device formed on a portion of a turbine shroud; and
a shroud ledge positioned proximate an aft portion of the turbine case
and spaced apart from the nozzle rail to form a shroud groove therebetween.
2. A turbine shroud, comprising:
a body having a forward rail and an aft rail; and
an anti-rotation device integrally formed in a portion of the forward rail.
3. The turbine shroud of claim 2, wherein the anti-rotation device comprises:
a base end coupled with the forward rail and separated from a first portion of the
forward rail adjacent a sidewall of the turbine shroud by a first gap;
a resilient portion extending from the base end and terminating in a free end, the
resilient portion separated from second portion of the forward rail adjacent the sidewall
by a second gap; and
a tab formed at the free end and configured to fit within and couple with a notch
formed in a nozzle rail of a split-line turbine case.
4. The turbine shroud of claim 3, wherein the tab further comprises:
an end surface separated from an adjacent third portion of the forward rail
by a third gap;
an angled surface coupled with and extending from the end surface;
a main surface coupled with and extending from the angled surface; and
a projection surface coupled with and extending orthogonally between the
resilient member and the main surface.
5. The turbine shroud of claim 4, wherein the second gap extends from the first gap past
the free end and parallel a forward edge of the forward rail.
6. The turbine shroud of claim 4, wherein the third gap is orthogonal to the second gap.
7. The turbine shroud, comprising:
an anti-rotation device having a resilient portion, the anti-rotation device oriented
in a direction of turbine blade rotation to prevent rotation of the turbine shroud with
respect to a split line turbine casing during engine operation.
8. A split line turbine casing, comprising:
a rail; and
an anti-rotation device formed in the rail, wherein the anti-rotation device
comprises:
a resilient portion extending from a base end and terminating in a free end,
the resilient portion separated from the rail by a gap; and
a tab formed at the free end and configured to fit within and couple with a
notch formed in a portion of a turbine shroud.